"NA" wrote in
:

I see no mention of switching off your charger. That is your most
likely source of a buzz.



Usually the source of this buzz is either corroded terminals or a dead
battery cell with the charger running full bore trying to bring the voltage
up. In either case, the high resistance the charger (or alternator which
makes the stereo whine at various pitches as the engine RPM varies) is
pumping into creates pulses on top of the residual battery voltage. As the
audio power amp is running directly off this pulsating voltage, the
buzz/whine is passed onto the speakers.

Does it whine when the alternator is running, too?